1. Field of the Invention
The present invention relates to the field of transistor driver circuits and in particular, to a versatile reduced swing differential signal, low voltage differential signal, mini low voltage differential signal, and bus low voltage differential signal interface circuit for backplane applications.
2. Description of Related Art
A variety of electronic devices, such as computers, monitors, flat panel displays, to name just a few, utilize high-speed differential data transmission in which the difference in voltage levels between two electronic signal lines form the transmitted signal. Differential data transmission is commonly used for data transmission rates greater than 100 Mbps over long distances, as well as in transfer of data to various display monitors such as LCD panels, notebook hosts to flat panel displays, and backplane rack-to-rack devices. Noise signals shift the ground level voltage and appear as common mode voltages. Thus, the detrimental effects of noise are substantially reduced.
To standardize such data transmission, a large variety of standards for interfaces have been developed. For example, one such standard is the TIA/EIA-644 standard low voltage differential signaling, LVDS, which is defined by the Electronics Industry of America, EIA and the Telecommunications Industry of America, TIA. This standard may operate in the Giga bit per second data rate range over a pair of signal lines. Driver circuits place signals on the lines. These driver circuits are intended to transmit differential signals with a nominal signal swing of 345 mV over the pair of transmission lines, which typically terminates in a single load of 100 ohms of resistance.
While the popularity of LVDS signaling is increasing every year, there are certain limitations, such as its limited common-mode range, and also its intended load of a single 100-Ohm termination. For this reason, LVDS-like signaling standards have been adopted for other applications. Other common signaling standards include Bus LVDS (BLVDS), reduced swing differential signaling (RSDS) and mini-low voltage differential signaling (mini-LVDS).
Bus LVDS extends the benefits of LVDS by targeting heavily loaded backplanes where card loading and spacing lowers the impedance of the transmission line as much as 50%. Therefore, the termination resistance for a BLVDS interface may vary from 40 to 200 ohms, while the nominal differential signal is 400 mV. The BLVDS interface can be used for multi-drop, multi-point, or point-to-point applications.
Reduced Swing Differential Signaling (RSDS) is a differential interface with a nominal signal swing of 200 mV. It retains the many benefits of the LVDS interface, such as high noise immunity, high data rate, low EMI characteristics, and low power dissipation. However, since RSDS applications are typically within a sub-system such as row/column drivers for an LCD screen, the signal swing is reduced from LVDS to lower power even further (hence the “Reduced Swing” or RS of the RSDS). RSDS is typically used in point-to-point or multi-drop application configurations.
Mini-LVDS is a new high-speed serial interface, which offers a low EMI, high bandwidth interface for display drivers, which is particularly well suited for thin film transistor (TFT) LCD panel column drivers. Mini-LVDS may be used for point-to-point and multi-drop applications.
While each interface standard has advantages, a designer must decide upon an appropriate standard at the very initial stages of a design, even though the basic function of the driver is the same regardless of the chosen standard. Many consequential decisions for designing an electronic device are then dictated by the standard chosen for the driver interface. The variety of receivers that will function properly with the predetermined standard interface is then limited in that the receiver must also adhere to the selected standard. As a result, manufacturers are required to stock different driver elements for each standard if they are to produce electronic products that happen to use different standard interfaces. This adds unnecessary restrictions and cost to a design.
Thus, there is a need to overcome the disadvantages of the prior art as discussed above, and in particular to provide a versatile RSDS, LVDS, mini-LVDS, and BLVDS driver for backplane applications.